Radiation-sensitive relief-forming materials having a suitable relief-forming material or layer are known in the art. An important advance in the art of making and using masking films to provide relief images in such materials is described in U.S. Patent Application Publication 2005/0227182 (Ali et al., hereinafter cited as U.S. '182). For example, this publication describes useful materials and methods for providing flexographic printing plates having a suitable relief image, using a thermally sensitive mask forming imageable material.
Thus, a relief image can be produced creating a mask, for example by thermal imaging a suitable masking film or element to provide the desired pattern (generally using an infrared radiation laser under computer control) through which a photocurable element is imaged, typically using ultraviolet radiation. For example, U.S. '182 describes means for forming an imaged mask material.
For example, the imaged mask material is placed in contact with a relief-forming material and subjected to overall exposure with actinic radiation (for example, UV radiation) to cure the relief-forming material in the unmasked areas and thus form a negative image of the imaged mask material in the relief-forming material. The imaged mask material can then be removed and the uncured regions on the relief-forming material are removed using a development process. After drying, the resulting imaged relief-forming material has a relief image that can be used for suitable printing operations.
Advances in imageable materials are described in U.S. Pat. No. 7,799,504 (Zwadlo et al.) for making imaged mask materials. These imageable materials have at least 5 layers coated onto a transparent substrate.
In materials having a relief image, such as flexographic printing plates, the combination of highlight dot retention and reverse line depths (RLD) define exposure latitude of an imaging system. Highlight dot retention is important for adequate fine resolution printing and adequate reverse line depths are important to provide clean line images with good separation in the resulting printed impressions (no halation). Typically, with increased exposure of the relief-forming material through the imageable material (mask), highlight retention is increased while reverse line depths are decreased.
There is a desire to use a considerably simpler design for such imageable materials used to form masks that can be used to provide excellent reverse line depths without compromising highlight dot retention.